Process for producing a halogenated butyl rubber

Abstract: A halogenated butyl rubber is prepared by a process wherein a monomer charge comprising isobutylene, and a conjugated diolefin having the formula wherein R₁, R₂ and R₃ which may be the same or different are a methyl group or a hydrogen atom and X is bromine or chlorine together with a initiator having the formula wherein each R₄ is an alkyl, aryl or aralkyl group, Y is preferably an alkoxy, hydroxy, peroxy ester or halide, and n is a positive whole number are introduced into a suitable reaction vessel in a specified ratio at a temperature of from about -90° to -10°C, a solution of a Lewis acid is added and the monomers are copolymerized at said temperature to form said halogenated butyl rubber, and the halogenated rubber is recovered from solution.

Description: Field of Invention This invention relates to a process for the preparation of halogenated butyl rubbers. More particularly, the present invention relates to a process whereby halogenated-type rubbers may be prepared directly by the copolymerization of the appropriate monomers. Background of the Invention The expression "butyl rubber" as employed herein is defined to include a copolymer of a C 4 to C 6 isolefin, preferably isobutylene, and a C 4 to C 8 conjugated diolefin, preferably isoprene. A preferred butyl rubber contains from 97 to 99.5 weight percent of isobutylene and from 0.5 to 3 weight percent of isoprene. The processes used to prepare butyl rubber are well known in the art. Commercially butyl rubber is prepared in a low temperature cationic polymerization process using Lewis acid type catalysts of which a typical example is aluminum trichloride. The process used most extensively employs methyl chloride as the diluent for the reaction mixture and the polymerization is conducted at temperatures of the order of less than -90°C. Methyl chloride is employed for a number of reasons, one being that it is a solvent for the monomers and aluminum trichloride catalyst and a nonsolvent for the polymer product and thus affords a slurry. Also, methyl chloride has suitable freezing and boiling points that permit, respectively, low temperature polymerization and effective separation of the methyl chloride from the product polymer and unreacted monomers. However, it is also possible to conduct such polymerizations in a diluent which is a solvent for the polymer produced, pentane, hexane, heptane and mixtures of the aforementioned solvents with one another or with methyl chloride and/or methylene chloride. Recovery of the butyl rubber is achieved by conventional techniques used to recover rubbery polymers inducing (i) contacting the polymer slurry or solution with steam and water thereby flashing off the diluent (ii) passing the aqueous slurry through a vibrating screen or rotary filter to separate the bulk of the water and (iii) passing the polymer through a tunnel drier or a series of extruders or both to completely remove all the water and occluded gases. Halogenated butyl rubber which can be either brominated butyl rubber or chlorinated butyl rubber is produced by the bromination or chlorination of the aforementioned butyl rubber. Brominated butyl rubber (bromobutyl rubber) typically contains from 1 to 3, preferably from 1 to 2, weight percent of isoprene and from 97 to 99, preferably from 98 to 99, weight percent of isobutylene, based on the hydrocarbon content of the rubber, and from 1 to 4, preferably from 1.5 to 3, weight percent of bromine, based on the bromobutyl rubber. Chlorobutyl rubber typically contains from 1 to 3, preferably from 1 to 2, weight percent of isoprene and from 97 to 99, preferably from 98 to 99, weight percent of isobutylene, based on the hydrocarbon content of the rubber and from 0.5 to 2.5, preferably from 0.75 to 1.75, weight percent of chlorine, based on the chlorobutyl rubber. Commercially halogenation of the butyl rubber is carried out in a hydrocarbon solution such as hexane using elemental chlorine or bromine in a 1:1 molar ratio relative to the enchained isoprene in the butyl feedstock. The solution of butyl rubber with the desired molecular weight and mole percent unsaturation in hexane may be prepared by one of two procedures; one involving dissolution of the slurry from a butyl polymerization reactor and the other involving dissolution of solid pieces of finished butyl rubber. In the former procedure the cold slurry in methyl chloride is passed into a drum containing hot liquid hexane which rapidly dissolves the fine slurry particles. The methyl chloride and the unreacted monomers are flashed off for recovery and recycle and the hot solution is adjusted to the desired concentration for halogenation, typically from 20 to 25 weight percent butyl rubber in an adiabatic flash step. In the latter procedure bales of finished butyl rubber, chopped or ground to small pieces, are conveyed to a series of agitated dissolving vessels and solutions containing from 15 to 20 weight percent butyl rubber are obtained in from 1 to 4 hours depending upon the temperature, particle size and amount of agitation. In the halogenation process the solution of butyl rubber is treated with chlorine or bromine at a temperature of from 40 to 65°C in one or more highly agitated reaction vessels, the chlorine being introduced as a gas or in dilute solution because of its rate of reaction with butyl rubber. Because of its lower rate of reaction bromine may be used in liquid or gaseous form. The hydrochloric or hydrobromic acid generated during the halogenation is neutralized with dilute aqueous base and the aqueous layer is subsequently removed by settling. Antioxidants or stabilizers are then added and the halogenated butyl rubber is then recovered in a manner similar to that used to recover butyl rubber. Investigations of the molecular structure of the halogenated butyl rubbers have shown that in current commercial halogenation procedures a number of allylic halides are produced by means of an ionic mechanism wherein a positively charged halogen atom is added to the double bond of the enchained isoprene and a proton alpha to the carbonium ion is subsequently abstracted by a negatively charged species resulting in a shift in the double bond. The major halogenated isomer produced both in the case of chlorobutyl rubber and bromobutyl rubber has been found to be the exomethylene allylic halide isomer. It is believed that these allylic halide structures in the halogenated butyl rubbers are the reason why the halogenated butyl rubbers exhibit enhanced cure compatibility with highly unsaturated elastomeric materials such as natural rubber, styrene-butadiene rubbers, polybutadiene rubbers and the like relative to butyl rubber. In view of the foregoing it would be advantageous if halogenated polymers with allylic halide functionality analogous to the halogenated butyl rubbers could be synthesized directly by the copolymerization of the appropriate monomers thereby leading to a reduction in costs associated with the process of halogenating butyl rubber. Description of the Prior Art U.S. Patent No. 3,067,182 (Giffin to Dow) discloses the copolymerization of from 70 to 99 mole percent of isobutylene with from 1 to 30 mole percent of isopropenylbenzyl chloride, preferably the para isomer, in an inert solvent using a Friedel-Crafts catalyst and a temperature below about -50°C to afford a uniform copolymer having reactive benzylic chloride groups. U.S. Patent 3,299,020 (Hunter et al to Esso) discloses a process for the copolymerization of an olefin with an allyl halide comprising forming a first solution by mixing 5 to 25 parts of methallyl chloride and the like with 95 to 75 parts of an alkyl halide solvent such as methyl chloride, methylene chloride and ethyl chloride at a temperature of from about -5 to about -40°C and adding thereto a Friedel-Crafts catalyst chosen from the group consisting of boron chloride, aluminum chloride, aluminum bromide and stannic chloride until a strong colour develops; forming a second solution comprising 10 to 35 parts by weight of an olefin and 65 to 90 parts by weight of an alkyl halide; and reacting said second solution with said first solution thereby providing a copolymer of high molecular weight and a high intrinsic viscosity. The copolymer obtained by the aforesaid process does not have allylic halide functionality and thus will not exhibit the enhanced cure compatibility that the halogenated butyl rubbers exhibit with highly unsaturated elastomeric materials. Sadykh-Zade et al in Dokl.Akad.Nauk Azerb. SSR 1968, 24(6) pages 20-23 (Chem. Abstr. 70, 20786j) state that chlorobutyl rubber may be prepared under conditions suitable for butyl rubber synthesis by copolymerizing (1) isobutylene and methallyl chloride in methyl chloride; (2) isobutylene, isoprene and methallyl chloride in methyl chloride; and (3) isobutylene and 2-chloromethyl-1,3-butadiene in methyl chloride, using aluminum chloride as catalyst. Copolymers containing up to two percent chlorine are reported to be obtained. U.S. Patent No. 4,074,035 (Powers et al to Exxon) discloses a continuous process for the preparation of gel-free interpolymers comprised of isobutylene and a mixture of from 0.5 to 5.0 mole percent meta- and para-chloromethyl styrene which consists of: (a) continuously feeding the monomers in the range of 2 to 20 parts by weight, from 80 to 98 parts by weight of a solvent in which the monomers and the interpolymers are soluble and from 0.001 to 0.05 parts by weight of a catalyst selected from the group consisting of ethyl aluminum dichloride, ethyl aluminum sesquichloride, diethyl aluminum chloride, or boron trifluoride to a reaction zone maintained at a temperature in the range of -120°C to -20°C to form a reaction mixture; (b) maintaining the reaction mixture in the reaction zone at the temperature for a time sufficient to convert at least one of the monomers to the interpolymer in an amount equal to or greater than 85 percent; and (c) recovering the interpolymer. Summary of the Invention It is an objective of this invention to provide a process whereby polyisobutylene-based polymers bearing allylic halide functionality analogous to halogenated butyl rubbers may be prepared directly by the copolymerization of the appropriate monomers. Accordingly, our invention provides a process for the preparation of a halogenated butyl rubber comprising the steps of: (A) introducing into a suitable reaction vessel a monomer charge comprising from 80 to 95 weight percent of isobutylene and from 5 to 20 weight percent of a conjugated diolefin bearing an allylic halide moiety characterized in that said conjugated diolefin bearing an allylic halide moiety has the formula wherein R 1 , R 2 and R 3 are selected from the group consisting of hydrogen and methyl groups and may be the same or different and X is selected from the group consisting of chlorine and bromine based on a total of 100 weight percent of said isobutylene and conjugated diolefin bearing an allylic halide moiety , and an initiator having the formula wherein each R 4 may be the same or different and is an alkyl, aryl or aralkyl group of 1 to 8 carbon atoms, Y is a carboxyl, alkoxyl, hydroxyl, halogen, hydroperoxide, peroxide or peroxy ester group and n is a positive whole number from 1 to 3 in an amount of from 1 x 10 -5 to 1 x 10 -3 moles per mole of said isobutylene at a temperature of from -90°C to -10°C. (B) adding a solution of from 1 X 10 -4 to 5 X 10 -2 moles of a Lewis acid per mole of isobutylene in an organic solvent to the reaction mixture of (A) at said temperature and polymerizing the monomers to form said halogenated butyl rubber, and (C) recovering the halogenated butyl rubber from the solution. Detailed Description of the Invention This invention is based upon the discovery that the copolymerization of isobutylene with an allylic halide substituted conjugated diolefin having a particular molecular structure under certain specific polymerization conditions permits the direct production of halogenated polymers with allylic halide functionality analogous to halogenated butyl rubbers. The monomer charge suitable for the practice of this invention comprises from 80 to 95 weight percent of isobutylene and from 5 to 20 weight percent of a conjugated diolefin bearing an allylic halide moiety based on a total of 100 weight percent of said isobutylene and said conjugated diolefin bearing an allylic halide moiety. The aforementioned conjugated diolefin is characterized in that it has the formula: wherein R 1 , R 2 and R 3 are selected from the group consisting of hydrogen and methyl groups and may be the same or different and X is selected from the group consisting of chlorine and bromine. Illustrative non-limiting examples of conjugated diolefins bearing an allylic halide moiety that are suitable for use in the present invention include 2-chloromethyl-4-methyl-1,3-pentadiene,2-bromomethyl-4-methyl-1,3-pentadiene,2-chloromethyl-3,4-dimethyl-1,3-pentadiene,2-chloromethyl-1,3-butadiene and 2-bromomethyl-1,3-butadiene,2-chloromethyl-4-methyl-1,3-pentadiene, 2-bromomethyl-4-methyl-1,3-pentadiene and 2-chloromethyl-3,4-dimethyl-1,3-pentadiene being preferred, and 2-chloromethyl-4-methyl-1,3-pentadiene being the monomer of choice. These compounds may generally be prepared by the pyrolysis of an appropriately substituted 2,5-dihydrothiophene-1,1-dioxide. For the sake of illustrative purposes, the preparation of 2-chloromethyl-4-methyl-1,3-pentadiene involves the pyrolysis of 3-chloromethyl-5,5-dimethyl-2,5-dihydrothiophene-1,1-dioxide, the dioxide being prepared by a multistep sequence involving the reduction of 3-carboethoxy-5,5-dimethyl-2, 5-dihydrothiophene with lithium aluminum hydride to the corresponding hydromethyl compound, subsequent chlorination with a mixture of triphenyl phosphine in carbon tetrachloride and then oxidation of the chloromethyl compound with m -chloroperbenzoic acid. The monomer charge suitable for use in the process of the present invention may further comprise a conjugated diolefin having from 4 to 8 carbon atoms in an amount of from 1 x 10 -2 moles to 1 x 10 -1 moles per mole of isobutylene. Preferably the conjugated diolefin is isoprene. The initiator suitable for use in the process disclosed herein has the formula wherein each R 4 may be the same of different and is an alkyl, aryl, or aralkyl group of 1 to 8 carbon atoms, Y is a carboxyl, alkoxyl, hydroxyl, halogen, hydroperoxide, peroxide or peroxy ester group and n is a positive whole number from 1 to 3 and the initiator is used in an amount of from 1 x 10 -5 to 1 x 10 -3 moles per mole of isobutylene. Illustrative non-limiting examples of suitable initiators include 1,4-di(2-methoxy-2-propyl) benzene, 1,3,5-tri(2-methoxy-2-propyl) benzene, 1,4-di(2-chloro-2-propyl) benzene, 1,3,5-tri(2-chloro-2-propyl) benzene, 2,6-dichloro-2,4,4,6-tetramethylheptane, 1,4-di(2-hydroxyl-2-propyl) benzene, 2,6-dihydroxyl-2,4,4,6-tetramethylheptane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3, 2,5-di(hydroperoxy)-2,5-dimethylhexane, 2,7-di(hydroperoxy)-2, 7-dimethyl octane, 1,4-di(2-hydroperoxide-2-propyl) benzene and 2,5-dimethyl-2,5-bis(benzoylperoxy) hexane. The initiator of choice is 2,5-dimethyl-2,5-bis(benzoyl peroxy) hexane. A number of Lewis acids are suitable for use in the process disclosed herein. Non-limiting examples include boron trichloride, boron trifluoride, aluminum trichloride, stannic tetrachloride, titanium tetrachloride, antimony pentafluoride and vanadium tetrachloride, with the Lewis acids of preference being boron trichloride and titanium tetrachloride. The amount of Lewis acid used relative to the amount of the initiator is not particularly critical. However, in order to be able to achieve more readily a polymer of the desired molecular weight, it is preferred that the mole amount of Lewis acid used is equal to or greater than the mole amount of the initiator used. Generally, it is preferred to use from 1 x 10 -4 to 5 x 10 -2 moles of a Lewis acid per mole of isobutylene. In the process of this invention, the Lewis acid is employed as a solution in a low freezing non-complex forming solvent selected from the group consisting of C 1 to C 4 halogenated hydrocarbons. Preferably, the solvent is selected from one of methyl chloride and methylene chloride. The inert organic solvents suitable for use in the commercial butyl rubber polymerizations mentioned previously are also suitable for use as the solvent for the monomer charge and the initiator in the process of the present invention. Preferred inert organic solvents include C 1 to C 4 halogenated hydrocarbons and mixtures thereof, C 5 to C 8 aliphatic hydrocarbons, C 5 to C 8 cyclic hydrocarbons, mixtures of one or more said halogenated hydrocarbons and one or more of said aliphatic hydrocarbons and mixtures of one or more said halogenated hydrocarbons and one or more of said cyclic hydrocarbons. Most preferably the inert organic solvent is selected from the group consisting of methyl chloride, methylene chloride, hexane and cyclopentane and mixtures thereof. While the order of addition of the monomer charge, the initiator, the Lewis acid and the inert organic solvent (if used) is not critical to the production of the polymers with allylic halide functionality, it is preferred that a suitable reaction vessel first be charged with the isobutylene and the conjugated diolefin bearing an allylic halide moiety (and the conjugated diolefin having from 4 to 8 carbon atoms if it forms part of the monomer charge), the initiator and the inert organic solvent (if used) at a temperature of from -90°C to -10°C. This is then followed by the addition of the solution of the Lewis acid in a halogenated hydrocarbon solvent to initiate the polymerization of the isobutylene and the conjugated diolefin bearing the allylic halide moiety (and the conjugated diolefin having from 4 to 8 carbon atoms if used). The monomers are polymerized at a temperature of from -90°C to -10°C to form a halogenated butyl rubber analogue. The polymer produced according to the process disclosed herein may be recovered by conventional techniques used to recover rubbery polymers. Such techniques include for the higher molecular weight polymers, contacting the polymer solution or slurry with copious amounts of hot water thereby flashing the inert organic solvent and any unreacted monomer. The polymer-hot water slurry may then be passed through a tunnel dryer or drying extruder. In another such technique, especially for polymers produced in the presence of an inert organic solvent and having a number average molecular weight of less than about 30,000, the polymer is recovered by (i) contacting the polymer solution or slurry with steam or by applying a vacuum to the polymer solution or slurry to flash off the solvent and any unreacted monomer; (ii) extracting acidic impurities and any remaining high boiling diluents with methanol; and (iii) drying the purified polymer to remove traces of methanol. In yet another technique, especially for low molecular weight polymers, the polymer solution is contacted with excess water to remove inorganic residues, the solution is dried and the inert organic solvent is then removed, as by evaporation. The products produced according to the process described herein are polymers bearing allylic halide functionality analogous to halogenated butyl rubbers. Evidence for the formation of such polymers is afforded by NMR spectroscopy. As an illustration the 250 MH z 1 H NMR spectrum of the product obtained upon the copolymerization of isobutylene with 2-chloromethyl -4-methyl-1, 3-pentadiene exhibits a number of signals that can be attributed to two different structures being present in the polymer. For, a singlet at 3.95 ppm can be attributed to the methylene protons attached to the same carbon atom as the chlorine atom PIB(Cl CH 2 )C=CH PIB and a singlet at 5.3 ppm can be attributed to a single olefinic proton PIB(ClCH 2 )C= CH PIB suggesting that the major structure in the copolymer arises from the 1,4-addition of 2-chloromethyl-4-methyl-1, 3-pentadiene monomer to the polyisobutylene cation. A minor structure in the copolymer appears to arise from 1,2-addition of the trisubstituted olefinic bond of the 2-chloromethyl-4-methyl-1, 3-pentadiene monomer to the polyisobutylene cation as a singlet at 4.0 ppm can be attributed to the methylene protons attached to the same carbon as the chlorine atom PIB(Cl CH 2 )C=CH 2 and the singlet at 5.2 ppm can be attributed to two olefinic protons attached to the same carbon atom of the olefinic bond PIB(ClCH 2 )C= CH 2 . While not wishing to be bound by any theories, it is believed that conjugated diolefins such as 2-chloromethyl-4-methyl-1,3-pentadiene wherein the olefinic bond that does not bear the allylic halide moiety bears at least two methyl substituents, that is at least both of R 1 and R 2 are methyl groups, upon copolymerization with isobutylene are incorporated into the copolymer to a greater extent relative to conjugated diolefins such as 2-chloromethyl-1,3-butadiene wherein the olefinic bond that does not bear the allylic halide moiety, is a terminal olefinic bond, in part because of the stabilization afforded the intermediate allylic cation by the methyl substituents. For this reason 2-chloromethyl-4-methyl-1,3-pentadiene,2-bromomethyl-4-methyl-1,3-pentadiene and 2-chloromethyl-3,4-dimethyl-1,3-pentadiene are the monomers preferred for copolymerization with isobutylene, and 2-chloromethyl-4-methyl-1,3-pentadiene is the monomer of choice for the production of a chlorinated butyl rubber. Experimental 1. Preparation of 2-Bromomethyl-1,3-Butadiene A) Bromination of 3-methyl sulfolene 3-Methyl-2,5-dihydrothiophene-1,1-dioxide (50.0 g, 0.38 mol), N-bromo-succinimide (74.1g, 0.42 mol) and chloroform (600 ml) were placed in a three-necked one litre round bottomed flask equipped with a mechanical overhead stirrer, a reflux condenser and a gas inlet. Argon gas was bubbled through the solution for 5 minutes and then benzoyl peroxide (4.60 g, 0.19 mol) was added and the mixture heated under reflux for eighteen hours during which time the solution first become orange in colour and then yellow. The solution was cooled to ambient temperature, washed with water (300 ml x 5) to remove the succinimide, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to afford a thick orange oil (11.4 g). The crude product was chromatographed using silica gel as the support and chloroform as the eluant and then recrystallized twice from 95 percent ethanol to give 3-bromomethyl-2,5 dihydrothiophene-1,1-dioxide. 9.6 g (12 percent yield). m.p. 76-84°C, 1 H NMR (300 MH z , CDCl 3 ): 6.11.(brs 1H), 4.05 (s,2H), 3.88 (s,4H); 13 C NMR (75 MH z ): 29.84, 56.53, 57.34, 122.28, 134.30. B) Pyrolysis of 3-Bromomethyl-2,5-Dihydrothiophene-1,1-Dioxide 3-Bromomethyl-2,5-dihydrothiophene-1,1-dioxide (22.0 g, 0.10 mol) was placed in a 100 ml round-bottomed flask which was connected to a short-path still and the system was evacuated to 1.5 mm Hg pressure. The flask was lowered into an oilbath which had been preheated to a temperature of about 170 to about 190°C while the receiver was cooled in a liquid nitrogen bath. After about 15 minutes the vacuum was released and the receiving flask was warmed to ambient temperature in a fume hood to allow the sulphur dioxide to escape. The distillate which was obtained as a light orange liquid was filtered through a short plug of basic alumina affording 2-bromomethyl-1,3-butadiene as a clear liquid. 10.10 g (67 percent yield) 1 H NMR (300 MHz, CDCl 3 ): 6.34 (dd, 1H), 5.5-5.2 (m, 4H), 4.11 (s,2H); 13 C NMR (75 MH z ): 30.65, 116.07, 120.30, 135.13, 142.49. Preparation of 2-Chloromethyl-4-Methyl-1, 3-Pentadiene A) Reduction of 3-Carboethoxy-5,5-Dimethyl-2,5-Dihydrothiophene 3-Carboethoxy-5,5-dimethyl-2, 5-dihydrothiophene (8.5 g, 0.046 mol) dissolved in dry tetrahydrofuran (100 ml) was placed in a 250 ml flask under a nitrogen atmosphere, and cooled in an ice-methanol bath to -10°C. Lithium aluminum hydride (0.90 g, 0.24 mol) was added slowly and the reaction mixture then stirred slowly for one hour before being quenched with saturated ammonium chloride (300 ml). The organic layer was removed and the aqueous layer was extracted with ether (150 ml x 3), the organic layers dried over anhydrous magnesium sulfate, filtered, concentrated and chromatographed (support silica gel 60, 70-230 mesh; column size: 40 x 200 mm; eluant: 40 percent ether in petroleum ether (35-60°C); fraction size: 20 ml). The product, 3-hydromethyl-5, 5-dimethyl-2, 5-dihydro-thiophene, was obtained as a liquid from fractions 8 to 20. 5.10 g (78 percent yield). IR (neat) 3351, 2956, 1666, 1456, 1109, 1026 cm -1 ; 1 H NMR (300 MH z , CDCl 3 ): 5.56 (S,1H), 4.19 (S,2H), 3.77 (S,2H), 2.0-1.9 (S,OH), 1.51 (S,6H); 13 C NMR (75 MH z , CDCl 3 ) 32.2, 38.1, 59.3, 61.5, 135.7, 138.9. B) Chlorination of 3-Hydroxymethyl-5,5-Dimethyl-2,5-Dihydrothiophene 3-Hydroxymethyl-5,5-dimethyl-2,5-dihydrothiophene (5.10 g, 0.035 mol) was added to a solution of triphenyl phosphine (11.13 g, 0.042 mol) in carbon tetrachloride (150 ml). The solution was heated under reflux for sixteen hours, cooled, diluted with 150 ml petroleum ether (35-60°C), filtered and concentrated. Column chromatography (support silica gel 60, 70-230 mesh; column size: 25 x 300 mm; eluant: 10 percent ether in petroleum ether; fraction size: 10 ml) gave a mixture of triphenyl phosphine and the desired product in fractions 2 to 8. Kugle Rohr distillation gave 3-chloromethyl 5,5-dimethyl-2, 5-dihydrothiophene as a clear liquid. 3.53 g (61 percent yield) Bp=90-100°C/15 mm Hg; IR (neat): 2957, 1663, 1265, 693cm -1 ; 1 H NMR (300 MH z CDCl 3 ): 5.67 (s,1H), 4.13 (s,2H), 3.83 (s,2H), 1.51(s,6H); 13 C NMR (75 MH z , CDCl 3 ): 32.0, 38.3, 42.5, 59.0, 135.0, 139.4. C) Oxidation of 3-Chloromethyl-5, 5-Dimethyl-2, 5-Dihydrothiophene. (Method I) 3-Chloromethyl-5, 5-dimethyl-2, 5-dihydrothiophene (17.84 g, 0.11 mol) was dissolved in methylene chloride (1.5 l) and cooled in an ice bath while 50 percent m -chloroperoxybenzoic acid (75.7 g, 0.22 mol) was added with stirring. The bath was warmed to ambient temperature over three hours and the reaction mixture was checked by 1 H NMR to ensure that the reaction was complete. The methylene chloride layer was washed with saturated sodium bicarbonate solution (400 ml x 6) and then with water (400 ml). The methylene chloride layer was dried over anhydrous magnesium sulphate, filtered and concentrated to afford a mixture of the desired product and m -chlorobenzoic acid. The desired product, the sulphone was purified by column chromatography (support silica gel 60, 70-230 mesh; column size: 40 x 400 mm; eluants: ether-petroleum ether (35-60°C) mixtures; the eluant being changed from 20 percent ether to 40 percent ether in the petroleum ether. After two chromatographic passes, 3-chloromethyl-5, 5-dimethyl-2, 5-dihydrothiophene-1, 1-dioxide was obtained. 17.2 g (80 percent yield). Mp 59-60°C; 1 H NMR (300 MH z , CDCl 3 ): 5.98 (br s, 1H), 4.12 (s,2H), 3.82 (s.2H), 1.47 (s,6H); 13 C NMR (75 MH z , CDCl 3 ): 21.5, 43.1, 54.2, 64.1, 130.3, 134.7. D) Oxidation of 3-chloromethyl-5,5-Dimethyl-2,5-Dihydrothiophene (Method II) 3-Chloromethyl-5,5-dimethyl-2,5-dihydrothiophene (3.50 g, 0.0215 mol) was dissolved in methylene chloride (150 ml) and cooled in an ice-bath while 80-85 percent m -chloroperoxybenzoic acid (9.74 g, 0.056 mol) was added. The reaction was followed by 1 H NMR and additional m -chloroperoxybenzoic acid (0.93 g, 0.005 mol) was added to ensure completion of the reaction. The suspension was filtered, the methylene chloride solution was washed with saturated sodium bicarbonate solution (50 ml x 4), dried over anhydrous magnesium sulphate, filtered and concentrated, yielding 3-chloromethyl-5,5-dimethyl-2,5-dihydrothiophene-1,1-dioxide as a thick oil. 4.0 g (96 percent yield) IR (neat) 2977, 1461, 1305, 1199, 1116, 771, 696, 612 cm -1 . 1 H NMR (300 MH z , CDCl 3 ): 5.98 (s,1H), 4.12 (s,2H), 3.82 (s,2H), 1.47 (s,6H); 13 C-NMR (75 MH z , CDCl 3 ): 21.6, 43.1, 54.2, 64.2, 130.3, 134.8. E) Pyrolysis of 3-Chloromethyl-5,5-Dimethyl-2,5-Dihydrothiophene-1,1-Dioxide Kugle Rohr distillation of the sulphone (2.00 g, 0.010 mol) at an air bath temperature of about 150°C and a pressure of about 130 to about 150 mm Hg afforded the product 2-chloromethyl-4-methyl-penta-1,3-diene as a light yellow liquid. 1.14 g (85 percent yield) IR (neat): 3091, 2973, 2933, 1654, 1629, 1444, 908, 745 cm -1 ; 1 H NMR (300 MH z , CDCl 3 ): 5.66 (q, 1H), 5.32 (d, 1H), 5.00 (s,1H), 4.03 (d, 2H), 1.83 (d,3H), 1.81 (d,3H); 13 C NMR (75 MH z , CDCl 3 ): 19.6, 26.6, 49.9, 116.7, 122.4, 138.0, 141.8. Example 1 Two random copolymerizations (1a and 1b) of isobutylene with 2-bromomethyl 1,3-butadiene were carried out in a dry box under a nitrogen atmosphere by charging screw-capped test tubes with specific amounts of each of a solvent, initiator 2,5-dimethyl-2,5-bis(benzoylperoxyhexane), isobutylene and 2-bromomethyl-1,3-butadiene at a temperature of about -70°C. Copolymerization was initiated by the addition of pure Lewis acid cocatalyst, in this instance a 1.0 M solution of titanium tetrachloride in methylene dichloride (2.0 ml), and allowed to proceed for 45 minutes during which time the screw capped test tubes were periodically agitated manually. The copolymerizations were quenched by the addition of methanol (5 ml) to each test tube. The resultant copolymers were recovered by first partially removing the solvent under reduced pressure and then coagulating copolymers by the addition of methanol. The copolymers were characterized by 250 MH z 1 H NMR spectroscopy and high pressure gel permeation chromatography using a Waters' instrument which was calibrated with narrow molecular weight distribution polystyrene standards, allowance being made for the fact the monomer being polymerized was isobutylene by using the polyisobutylene [K] and a values in the Mark-Houwink equation [η] = KM a . The copolymerization parameters and the physical properties of the resultant copolymers are provided in Table I. From the 1 H NMR spectroscopic results in Table I it can be seen that while 2-bromomethyl-1,3-butadiene was incorporated into the polyisobutylene, it was at a low level. Example 2 Two random copolymerizations (2a and 2b) of isobutylene with 2-chloromethyl-4-methyl-1,3-pentadiene were carried out using the same procedure as that described in Example 1. The copolymerization parameters and the physical properties of the resultant copolymers are provided in Table II. From the 1 H NMR spectroscopic results in Table II it can be seen that under the particular experimental conditions used copolymerization of isobutylene with 2-chloromethyl-4-methyl-1,3-pentadiene afforded a copolymer wherein the chlorinated monomer was incorporated at levels of up to 3.5 mole percent. While not wishing to be bound by any theories, it is believed that 2-chloromethyl-4-methyl-1,3-pentadiene is incorporated into the copolymer to a greater extent relative to the incorporation of 2-bromomethyl-1,3-butadiene in part because of the stabilization afforded the intermediate allylic cation by the two methyl substituents on the olefinic bond that does not bear the allylic chloride functionality. A preliminary study of the response of the chlorinated polymer to zinc oxide curing was then carried out using the following formulation and conditions. Chlorinated polymer 3.0 g Zinc Oxide 0.15 g Stearic acid 0.06 g Temperature 165°C Time 15 minutes Upon treatment in this manner it was found that the polymer was extensively cross-linked as evidenced by its lack of solubility in cyclohexane. Example 3 Two random terpolymerizations (3a and 3b) of isobutylene with 2-chloromethyl-4-methyl-1,3-pentadiene and isoprene were carried out using the same procedure as that described in Example 1. The terpolymerization parameters and the physical properties of the resultant terpolymers are provided in Table III. From the results in Table III it can be seen that under the particular experimental conditions used, terpolymers of isobutylene, isoprene and 2-chloromethyl-4-methyl-1,3-pentadiene were formed.

Claims: A process for the preparation of a halogenated butyl rubber comprising the steps of: (A) introducing into a suitable reaction vessel a monomer charge comprising from 80 to 95 weight percent of isobutylene and from 5 to 20 weight percent of a conjugated diolefin bearing an allylic halide moiety based on a total of 100 weight percent of said isobutylene and conjugated diolefin bearing an allylic halide moiety, which conjugated diolefin bearing an allylic halide moiety has the formula wherein R 1 , R 2 and R 3 are selected from the group consisting of hydrogen and methyl groups and may be the same or different and X is selected from the group consisting of chlorine and bromine, and an initiator having the formula wherein each R 4 may be the same or different and is an alkyl, aryl or aralkyl group of 1 to 8 carbon atoms, Y is a carboxyl, alkoxyl, hydroxyl, halogen, hydro peroxide, peroxide or peroxy ester group and n is a positive whole number from 1 to 3 in an amount of from 1 x 10 -5 to 1 x 10 -3 moles per mole of said isobutylene at a temperature of from -90°C to -10°C, (B) adding a solution of from 1 x 10 -4 to 5 x 10 -2 moles of a Lewis acid per mole of isobutylene in an organic solvent to the reaction mixture of (A) at said temperature and polymerizing the monomers to form said halogenated butyl rubber, and (C) recovering the halogenated butyl rubber from the solution. The process of Claim 1 wherein the conjugated diolefin bearing the allylic halide moiety is selected from the group consisting of 2-chloromethyl-4-methyl-1,3-pentadiene,2-bromomethyl-4-methyl-1,3-pentadiene and 2-chloromethyl-3,4-dimethyl-1,3-pentadiene. The process of Claim 1 wherein the monomer charge further comprises a conjugated diolefin having from 4 to 8 carbon atoms in an amount of from 1 x 10 -2 moles to 1 x 10 -1 moles per mole of isobutylene. The process of Claim 1 wherein said initiator is selected from the group consisting of 1,4-di(2-methoxy-2-propyl)benzene, 1,3,5-tri(2-methoxy-2-propyl) benzene, 1,4-di(2-chloro-2-propyl)benzene, 1,3,5-tri(2-chloro-2-propyl) benzene, 2,6-dichloro-2,4,4,6-tetramethylheptane, 1,4-di(2-hydroxyl-2-propyl) benzene,2,6-dihydroxyl-2,4,4,6-tetramethylheptane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3, 2,5-di(hydroperoxy)-2,5-dimethylhexane,2,7-di(hydro-peroxy)-2,7-dimethyloctane, 1,4-di(2-hydroperoxy-2-propyl)benzene and 2,5-dimethyl-2,5 bis(benzoylperoxy) hexane. The process of Claim 1 wherein the Lewis acid is selected from the group consisting of boron trichloride, boron trifluoride, aluminum trichloride, stannic tetrachloride, titanium tetrachloride, antimony pentafluoride and vanadium tetrachloride. The process of Claim 5 wherein the Lewis acid is selected from the group consisting of boron trichloride and titanium tetrachloride. The process of Claim 1 characterized in that it is conducted in an inert organic solvent selected from the group consisting of C 1 to C 4 halogenated hydrocarbons, C 5 to C 8 aliphatic hydrocarbons, C 5 to C 8 cyclic hydrocarbons, mixtures of one or more said halogenated hydrocarbons and one or more said aliphatic hydrocarbons and mixtures of one or more said halogenated hydrocarbons and one or more said cyclic hydrocarbons. The process of Claim 7 wherein said inert organic solvent is selected from the group consisting of methyl chloride, methylene chloride, hexane and cyclopentane and mixtures thereof. The process of Claim 1 wherein the organic solvent of step (B) is selected from the group consisting of methyl chloride and methylene chloride. A process for the preparation of a chlorinated butyl rubber comprising the steps of: (A) introducing into a suitable reaction vessel a monomer charge comprising from 80 to 95 weight percent of isobutylene and from 5 to 20 weight percent 2-chloromethyl-4-methyl-1,3-pentadiene based on a total of 100 weight percent of said isobutylene and 2-chloromethyl-4-methyl-1,3-pentadiene, from 1 x 10 -2 to 1 x 10 -1 moles of isoprene per mole of isobutylene, an initiator having the formula wherein each R 4 may be the same or different and is an alkyl, aryl or aralkyl group of 1 to 8 carbon atoms, Y is a carboxyl, alkoxyl, hydroxyl, halogen, hydroperoxide, peroxide or peroxy ester group and n is a positive whole number from 1 to 3 in an amount of from 1 x 10 -4 to 1 x 10 -2 moles per mole of said isobutylene and an inert organic solvent comprising a mixture of methyl chloride and hexane at a temperature of from -90°C to 0°C, (B) adding a solution of from 4 x 10 -4 to 1 x 10 -1 moles of titanium tetrachloride per mole of isobutylene in methylene chloride to the reaction mixture of (A) at said temperature and polymerizing the monomers to form said chlorinated butyl rubber, and (C) recovering the chlorinated butyl rubber from the solution.

Inventors: OSMAN AKHTAR, OSMAN, AKHTAR
Applicants: BAYER INC, BAYER INC.
Application year: 1994
Main classification: C08F210
IPC codes: C08F2, C08F10, C08F210